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题库 / Prep2008E2-CR-92
Kate: The recent decline in numbers of the Tennessee warbler, a North American songbird that migrates each fall to coffee plantations in South America, is due to the elimination of the dense tree cover that formerly was a feature of most South American coffee plantations.
Scott: The population of the spruce budworm, the warbler's favorite prey in North America, has been dropping. This is a more likely explanation of the warbler's decline.
Which of the following, if true, most seriously calls Scott's hypothesis into question?
The numbers of the Baltimore oriole, a songbird that does not eat budworms but is as dependent on South American coffee plantations as is the Tennessee warbler, are declining.
The spruce budworm population has dropped because of a disease that can infect budworms but not Tennessee warblers.
The drop in the population of the spruce budworm is expected to be only temporary.
Many Tennessee warblers have begun migrating in the fall to places other than traditional coffee plantations.
Although many North American songbirds have declined in numbers, no other species has experienced as great a decline as has the Tennessee warbler.
A是一个类比。要驳斥第二个人的论调，说更可能是因为没虫子鸟才不去的论调。就要证明这虫子不影响鸟儿。A里面说另一种Songbird跟这个Tennessee warbler都一样在此地生活（作类比），他们数量减少了，但是他们不吃虫子。既然虫子因素对这Songbird不起作用，那鸟儿数量减少就肯定是因为别的原因。再类比到Tennessee warbler身上，所以这就大大削弱了原句里的那个argument。
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